It is known that in some medical procedures, such as inter- and post-operative autotransfusion, there is the need to separate the plasma from the red cells of the blood aspirated from the operating area, so as to make them available for re-infusion to the patient. It is also known that currently this procedure is performed in centrifugation cells in which the blood is introduced by means of a peristaltic pump.
A centrifugation cell substantially comprises two bells which are mutually coaxial and rigidly coupled, and the portion of space between them is connected to the outside by means of two tubes, an inlet tube and an outlet tube, which are connected to the bells by means of a rotary coupling. The two bells are turned about their own axis, while the tubes are kept motionless.
The procedure provides for a first step for filling the cell, in which the blood is introduced by means of the inlet tube. Due to the centrifugal force, the red cells, which are the heaviest cellular components of blood, are propelled outward, compacting against the wall of the outer bell. Other cellular components such as white blood cells and platelets are arranged in a thin layer known as buffy coat directly adjacent to the mass of compacted red blood cells. The separated plasma, the remaining component of blood, is arranged in a layer which lies above the buffy coat. The plasma, which contains various substances such as anticoagulant, free hemoglobin and other substances from the operating field, will be referenced hereinafter as “supernatant”.
As filling continues, the buffy coat moves closer to the rotation axis, displacing the supernatant toward the outlet tube of the cell. When the supernatant reaches the outlet tube the supernatant flows out of the cell into an adapted collection bag.
The flow of the supernatant in the outlet tube continues until an optical detector reports that the buffy coat has reached the outlet tube of the cell. At this point the filling step has ended and the introduction of new blood into the cell ends. The cell now contains compacted red cells and supernatant, which must be eliminated since it cannot be re-infused to the patient together with the red cells.
The above-described filling step is followed by a washing step performed by means of a washing solution which, when introduced into the cell, gradually takes the place of the supernatant that is expelled. At the end of the washing step the cell contains red cells and washing solution, i.e., substances suitable to be re-infused to the patient. The contents of the cell are collected in a suitable bag in a third step of the procedure, known as emptying.
Our attention is focused exclusively on the washing step, which is currently performed in manners that are not entirely satisfactory. A first procedure adopted in the background art provides for introducing in the cell a preset amount of washing solution at a value that is assuredly more than sufficient to wash the supernatant. The consequent oversizing, however, wastes time and washing solution.
Another procedure used in the art provides a transparency sensor on the outlet duct. However, this sensor is not able to detect the passage of transparent components of the supernatant such as the anticoagulant, and therefore does not provide entirely satisfactory results.